Tilt of Stationary Capsule in Pipe

When a cylindrical capsule moved by a liquid flowing in a pipe is stopped by the presence of an obstacle or protrusion on the pipe floor, the capsule may tilt in the pipe. This paper presents both an analysis and some experimental data to clarify and predict the minimum velocity required to cause capsule tilt. Capsules of three different aspect ratios and three diameter ratios were tested in a small (50.8 mm inside diameter) pipe loop. The experimental values of the capsule drag coefficient compared well with those from theory and a previous test. Data were used to calculate the lift moment coefficient and the critical tilt Froude number needed for predicting capsule tilt. Three large capsules with six different specific gravities were also tested in a large (190 mm inside diameter) pipe. Data for both small and large capsules showed good correlation between lift moment coefficient and tilt Froude number. It is shown that in some cases the capsule incipient velocity is governed by the critical tilt velocity.